This invention relates to a Stirling refrigerating machine in which a compressor is connected to an expander through a connection pipe, and particularly relates to improvements of a sealing structure provided at a joint between the compressor and the connection pipe.
A free displacer type Stirling refrigerating machine has been conventionally known as one of small size refrigerating machines which produce cold conditions at an extremely low temperature level. Such a refrigerating machine is disclosed in Japanese Patent Application Laid-Open Gazette No. 6-174321. The refrigerating machine is so composed that a compressor for compressing a gas refrigerant and an expander for expanding the gas refrigerant discharged from the compressor are connected to each other through a connection pipe.
Below, description will be made about the structure of the compressor.
As shown in FIG. 6, the compressor (a) includes a gastight casing (b), a cylinder (c) provided in the casing (b), a pair of pistons (e, e) reciprocatably fit in the cylinder (c) to form a compression room (d) in the cylinder (c), and linear motors (f, f) for reciprocating the pistons (e, e) respectively. The cylinder (c) has cylindrical recesses (c1, c1). The recesses (c1, c1) are formed around the compression room (d) in a manner coaxial with the cylinder (c).
The linear motor (f) has an annular permanent magnet (g) disposed in the recess (c1). The permanent magnet (g) generates a magnetic field with the cylinder (c) serving as a yoke. An inverted-cup-shaped bobbin (h) is reciprocatably placed in the recesses (c1). The bobbin (h) is provided with a drive coil (i). The drive coil (i) is opposed to the permanent magnet (g). The bobbin (h) is fixed at a center thereof to the piston (e). A lead (k) for supplying a current to the drive coil (i) is led out of the bobbin (h). The lead (k) is connected to a terminal (m) mounted on the casing (b). The outer bottom surface of the bobbin (h) (a side opposite to the piston) and the inner bottom surface of the casing (b) are bridged with a piston spring (j) formed of a coil spring. The piston spring (j) resiliently supports the piston (e) so as to allow reciprocating motions of the piston (e).
A gas passage (c2) is formed in the cylinder (c) and the casing (b). The gas passage (c2) is open at one end thereof to the compression room (d) and at the other end to the outer surface of the casing (b).
The compressor (a) is connected to one end of a connection pipe (n), so that the internal passage of the connection pipe (n) is communicated with the gas passage (c2). The other end of the connection pipe (n) is connected to an expander (not shown).
In operating the refrigerating machine, an alternating current of a specific frequency is supplied to the drive coils (i, i) through the leads (k, k). Thereby, a magnetic field generated around the drive coils (i, i) acts to reciprocate the bobbins (h, h). Attendantly, the pistons (e, e) lineally reciprocate in the cylinder (c) in opposite directions, so that a compressed gas generates in the compression room (d) in cycles. A pressure of a gas refrigerant thus compressed is introduced to the expander through the connection pipe (n). Thus, a high pressure and a low pressure repeatedly acts on the expander. In the expander, a gas refrigerant is expanded so that a cold condition is produced.
In such kind of refrigerating machine, it is required to maintain its operating performance at a high level. To satisfy the requirement, a compressed gas generated in the compressor (a) must be efficiently transferred to the expander. To cope with this, necessary positions surrounding the gas passage (c2) each have a sealing structure for preventing a leakage of a compressed gas.
Below, the conventional sealing structure will be described.
As shown in FIG. 7, O-rings (o, p, p) are disposed at a joint between the casing (b) and the connection pipe (n) and a contact part between the casing (b) and the cylinder (c), respectively. First, description is made about the sealing structure of the joint between the casing (b) and the connection pipe (n). A mount (b1) having a plain mounting surface is formed on the outer surface of the casing (b), while a plate-shaped flange (n1) is formed at one end of the connection pipe (n). A sealing groove (n2) is formed on the flange (n1). The sealing groove (n2) is annular and surrounds the internal passage of the connection pipe (n). A single O-ring (o) is inserted in the sealing groove (n2). The mount (b1) and the flange (n1) each have unshown screw holes. The gas passage (c2) is aligned with the internal passage of the connection pipe (n), and in this state the flange (n1) is brought into contact with the mounting surface of the mount (b1). Thereafter, screws (q, q) are screwed in both the screw holes, so that the connection pipe (n) is connected to the compressor (a). In this structure, since the single O-ring (o) is interposed between the flange (n1) and the mount (b1), this prevents a gas refrigerant flowing through the gas passage (c2) from leaking out of a clearance between the flange (n1) and the mount (b1) (See arrow A in FIG. 7).
Next, description is made about the sealing structure of the contact part between the casing (b) and the cylinder (c). Sealing grooves (c3, c3) are formed at both sides (right and left in FIG. 7) of the gas passage (c2) of the cylinder (c). The sealing grooves (c3, c3) are formed over the circumference of the cylinder (c). The cylinder (c) is inserted into the casing (b) with O-rings (p, p) (two in total) fit into the sealing grooves (c3, c3) respectively. In this structure, the two O-rings (p, p) are interposed between the outer periphery of the cylinder (c) and the inner periphery of the casing (b). Accordingly, a gas refrigerant flowing through the gas passage (c2) is prevented from leaking out of a clearance between the cylinder (c) and the casing (b) to the inner space of the casing (b) (See arrow B in FIG. 7).
However, the above sealing structure has the following problems: In the structure, a sealed part between the casing (b) and the cylinder (c) is formed over the circumference of the cylinder (c). In other words, the O-rings (p, p) each having a large diameter identical with the outer diameter of the cylinder (c) are used. Therefore, a sealed area becomes large. This makes it difficult to obtain a sufficient reliability of a sealing function, that is, the possibility that a gas refrigerant may leak out of the contact part between the casing (b) and the cylinder (c) to the inner space of the casing (b) is increased.
The present invention has been made in view of the above problem. An object of the invention is to increase a reliability of a sealing function of a contact part between a casing and a cylinder in a compressor of a Stirling refrigerating machine.
In the present invention, an end part of a connection pipe is inserted into insertion holes formed in a casing and a cylinder respectively. Then, a sealing function is provided to a joint between the end part of the connection pipe and the cylinder. In this arrangement, a sealed area is decreased, resulting in increase in reliability of the sealing function of the contact part between the casing and the cylinder.
More specifically, a solution taken in claim 1 of the invention is described below. As shown in FIGS. 1 and 3, the solution is directed to a Stirling refrigerating machine having a compressor (1) and an expander (2). The Stirling refrigerating machine premises the following structure: The compressor (1) comprises, a cylinder (4) fit into a casing (3), a piston (6) which is inserted into the cylinder (4) so as to be capable of reciprocating motion relative to the cylinder (4) and forms a compression room (7) between the piston (6) and the cylinder (4), resilient means (14) for resiliently supporting the piston (6) on the casing (3), and drive means (10) for driving the piston (6) into reciprocating motion relative to the cylinder (4). The compression room (7) is communicated with the expander (2) through a connection pipe (9). The drive means (10) relatively reciprocates the piston (6) with respect to the cylinder (4) so that a compressed fluid generated in the compression room (7) is introduced into the expander (2) through the connection pipe (9).
The casing (3) has an insertion hole (3c) which penetrates the casing (3) and whose one end is open to an outer surface of the casing (3), while the cylinder (4) has an insertion hole (4e) which is communicated at one end with the insertion hole (3c) of the casing (3) and at the other end with the compression room (7).
Further, a compressor (1) side joint end part of the connection pipe (9) is inserted into the insertion hole (3c) of the casing (3) and the insertion hole (4e) of the cylinder (4) to communicate an internal passage (9f) of the connection pipe (9) with the compression room (7).
Furthermore, sealing means (02, 28) are interposed between the compressor (1) side joint end part of the connection pipe (9) and the insertion hole (4e) of the cylinder (4).
A solution taken in claim 2 of the invention is so composed that in the Stirling refrigerating machine of claim 1, as shown in FIG. 3, an annular sealing groove (9d) is formed on one of the outer periphery of the connection pipe (9) located in the insertion hole (4e) of the cylinder (4) and the inner periphery of the insertion hole (4e) of the cylinder (4) so as to extend in a circumferential direction of the periphery. The sealing means is formed of an O-ring (02) fit into the sealing groove (9d).
A solution taken in claim 3 of the invention has, in the Stirling refrigerating machine of claim 1, the following structure: As shown in FIG. 4, the cylinder (4) is provided with a gas passage (8) coaxial with the insertion hole (4e) of the cylinder (4) and having a smaller diameter than the insertion hole (4e) of the cylinder (4). The gas passage (8) is communicated at one end with the compression room (7) and at the other end with the insertion hole (4e) through a step part (4f). The inner periphery of the insertion hole (4e) of the cylinder (4) is formed into a female thread (4g), while the outer periphery of the compressor (1) side joint end part of the connection pipe (9) located in the insertion hole (4e) of the cylinder (4) is formed into a male thread (9e) screwed in the female thread (4g). The sealing means is formed of an O-ring (02) interposed between the end surface of the connection pipe (9) and the step part (4f).
A solution taken in claim 4 of the invention has, in the Stirling refrigerating machine of claim 1, the following structure: As shown in FIG. 5, the inner periphery of the insertion hole (4e) of the cylinder (4) is formed into a female thread (4g), while the outer periphery of the compressor (1) side joint end part of the connection pipe (9) located in the insertion hole (4e) of the cylinder (4) is formed into a male thread (9e) screwed in the female thread (4g). The sealing means is made of an adhesive agent (28) put in a clearance between the female thread (4g) and the male thread (9e).
A solution taken in claim 5 of the invention is so composed that in the Stirling refrigerating machine of claim 1, as shown in FIGS. 4 and 5, the connection pipe (9) has a flange (9a) formed in one piece with the connection pipe (9) and opposed to the outer surface of the casing (3) and a metal packing (27) is interposed between the outer surface of the casing (3) and the flange (9a).
In the above-mentioned feature of claim 1 of the invention, when the Stirling refrigerating machine is in operation, the drive means (10) causes reciprocating motion of the piston (6) relative to the cylinder (4), so that a pressure of fluid compressed in the compression room (7) is introduced into the expander (2) through the connection pipe (9). In this operating condition, the sealing means (02), (28) interposed between the compressor (1) side joint end part of the connection pipe (9) and the insertion hole (4e) of the cylinder (4) prevent the fluid from leaking out of a clearance between the connection pipe (9) and the cylinder member (4). A sealed area of the sealing means (02), (28) is a contact part between the connection pipe (9) and the insertion hole (4e) of the cylinder (4). Thus, the sealed area is limited to a small area of only a part of the outer periphery of the connection pipe (9) thereby implementing high-reliable sealing.
In the features of claims 2, 3 and 4 of the invention, specific structures of the sealing means (02), (28) are obtained and thereby improves the practicality of the sealing structure. Particularly, in the features of claims 3 and 4 of the invention, the male thread (9e) formed on the outer periphery of the connection pipe (9) is screwed in the female thread (4g) formed on the cylinder (4). This eliminates the need for separate screw structure or the like for mounting the connection pipe (9) on the cylinder (4). Further, in the feature of claim 4 of the invention, the sealing means is made of an adhesive agent (28). This allows the sealing means to display the function of increasing a strength of mounting the connection pipe (9) on the cylinder (4) as well as the sealing function.
In the feature of claim 5 of the invention, the function of sealing between the connection pipe (9) and the casing (3) is displayed by the metal packing (27) interposed between those members. This provides high sealing performance to the joint of the connection pipe (9) to the compressor (1) in association with the actions of the other claims above-mentioned of the invention.
According to claim 1 of the invention, an area sealed by the sealing means (02), (28) can be limited to a small area of only a part of the outer periphery of the connection pipe (9). This implements a more secure sealing as compared with the conventional case of providing sealing means over the entire circumference of the cylinder (4). Consequently, the reliability of the sealing function can be increased, thereby maintaining the operating performance of the refrigerating machine at a high level.
According to claims 2, 3 and 4 of the invention, the practicality of the sealing structure can be increased. In particular, according to claims 3 and 4 of the invention, a simple joint structure and a simple joint work of the connection pipe (9) can be implemented. Further, according to claims 3 and 4, a joint structure can be formed between the inner periphery of the insertion hole (4e) of the cylinder (4) and the outer periphery of the connection pipe (9). This eliminates the need for providing a large flange to be joined to the casing on the outer periphery of the connection pipe as in the conventional case. In addition, there is no need for providing, in the casing, a mount and screw holes for joint of the flange. Accordingly, the thickness of the casing can be decreased, resulting in downsizing and weight reduction of the entire compressor. Furthermore, according to claim 4 of the invention, the sealing means can have a function of increasing a strength of mounting the connection pipe (9) on the cylinder (4) as well as the sealing function. Consequently, the joint of the connection pipe (9) can secure the high reliability of the joint state.
According to claim 5 of the invention, in association with the above effects of the claims, the joint of the connection pipe (9) to the compressor (1) can obtain high sealing performance. This further increases the operating performance of the refrigerating machine.